Herein, related art is discussed to aid in understanding the invention. Related art labeled “prior art” is admitted prior art; related art not labeled “prior art” is not admitted prior art.
One of the classic challenges for information technology (IT) managers is to insure that they have capacity for their peak computational loads. As a result, they may typically have low utilization of their computers (for example 25% of capacity) except for the rare occurrence of 100% peak. For example, an Internet service provider (ISP), such as AOL, may have peak usage of their web servers once a day during the late evening hours since most of their clients surf the web after dinner. The ISP has their servers on all the time consuming power even though utilization during most of the day may be less than 25% of the capacity; as a result, at least 75% of the power is wasted. In addition, servers are usually not turned off or put in sleep mode (as is done with laptops) when not in use so that servers can be activated instantaneously on demand.
To deal with this, IT managers have done the following: 1) they buy enough computers to deal with peak demands; the disadvantage of this is that full power is being used by computers even though they are just partially utilized; 2) they use “Instant Capacity” (ICAP, available from Hewlett-Packard Company) and comparable solutions that allow them to add processors based on demand; the disadvantage is that while the data center owner is not paying for the unused hardware, it is still paying for the power consumed by it; and 3) they buy computers to deal with the average loads; the disadvantage of this is that the IT manager's company then cannot support peak demand and thus loses revenue.
For economic and energy-conservation purposes, it would be beneficial to improve the match between workload and resources. This can mean getting more done with the resources available, more accurately matching resource requirements to energy consumption, or freeing unneeded resources for inactivation so that energy consumption can be reduced. One way to do this is to select optimal power versus performance modes based on feedback from utilization monitors. For example, if utilization of a processor is 50% when it is in high-performance mode, its clock speed can be lowered to achieve a higher utilization ratio and a more-than-proportional reduction in electrical energy usage. Concomitantly, power can be reallocated among components based on utilization. However, such methods are not optimal.